Indianapolis rookie quarterback Andrew Luck must make good-faith efforts to work exclusively with Colts sponsors before signing marketing deals with competing companies under the terms of the contract he signed with the club, according to sources familiar with the deal.

Fellow rookie quarterbacks Robert Griffin III, with Washington, and Miami’s Ryan Tannehill have similar language in their contracts, sources said, and agents for all three quarterbacks struggled with the clubs during contract negotiations to make the language less restrictive, if not eliminate it all together.

While language regarding an NFL player’s ability to promote and market himself varies from club to club, agents said there has been a move across the league to make it more restrictive in recent years, and especially this year.

Asked why, some agents said they thought it was an acceleration of a trend by clubs to try and control a player’s image off the field. One agent said he thought such clauses could help clubs secure more lucrative sponsorships with companies if there were more favorable terms for the companies to sign the athlete to a deal, as well.

As a matter of course, agents usually negotiate with the sponsors of the team that employs the player, but the contract language can give the club sponsor a better shot at signing the athlete, agents said.

Luck’s agent, Will Wilson, executive vice president of football operations for Wasserman Media Group, declined to discuss the details of the quarterback’s contract but said, “The language that we agreed on is mutually acceptable and is designed to exploit synergies with the team where they exist but in no way limits Andrew’s ability to sign endorsements.”

Ben Dogra, CAA Football co-head and agent to Griffin, would not comment.

Pat Dye, Tannehill’s agent, said, “There is some obligation to use best efforts to work with team sponsors, but there is nothing preventing him from working with a company that is not a team sponsor.”

It was unclear, sources said, how it would be decided (or by whom) if there’s a dispute about whether a player used good-faith efforts—or, in Tannehill’s case, “best efforts”—to reach a deal with a team sponsor.

Dolphins spokesman Harvey Greene said the club does not comment on contracts. Redskins spokesman Tony Wyllie declined to comment. Colts spokesman Avis Roper said the team does not comment on player contracts.

SportsXchange.com first reported in June that one of the hold-ups in the Colts signing Luck was the club’s proposal to add language restricting potential marketing deals for him. Colts owner Jim Irsay, via Twitter, disputed the report and said Luck would be signed soon. Luck and the Colts agreed to a deal on July 19.

Former Colts quarterback Peyton Manning was not restricted as much by the language in his contract with the club, nor by the language in the contract he signed this offseason with Denver. Agents said such restrictions were not common when Manning entered the league in 1998. Further, because of the demand among clubs for Manning as a free agent, teams didn’t have the leverage to negotiate restrictions on his ability to sign marketing deals the same way they can with players who have less market demand.

CAA Football co-head Tom Condon, who represents Manning on the field, and IMG senior vice president Alan Zucker, who represents him in off-the-field endeavors, declined to comment.